The use of metallocene and Ziegler-Natta catalysts for the production of linear polyethylene and polypropylene polymers and waxes is well known in the art and the conditions to produce branched and linear waxes using single site metallocene catalysts have been described extensively. Typically, when Ziegler-Natta catalysts are used, waxes are produced by carrying out reactions at high temperatures (100-200° C.) in the presence of hydrogen as chain transfer agent. Reactions involving metallocene catalysts occur at lower temperatures and the degree of polymerisation is controlled by controlling the ratio of co-catalyst or activator to the polymerisation catalyst.
Specific examples in the prior art for the production of waxes include US 2003/171481 that discloses the synthesis of a functionalised wax based on vanadium and metallocene catalysts. JP 2003286308 discloses the use of metallocene catalysts with cyclopentadienyl backbones as ligands for the synthesis of narrow polydispersity polyolefin waxes of ethylene and propylene. Similarly, U.S. Pat. No. 5,023,388 discloses a process of synthesising a wax with narrow polydispersity using a metallocene catalyst. Last mentioned document discloses that hydrogen is used to regulate the molecular weight. In another example of a typical Ziegler-Natta based process (GB1444736), controlled polymerisation was conducted in the presence of the catalyst combinations TiCl4/Mg(OEt)2/AlEt3 or Ti(O-i-Pr)4/Mg(OEt)2/AlEt3/SiCl4 and hydrogen.
Waxes produced using single site catalysts have a molecular weight range between 500 and 5000 g.mol−1 (JP 2003201436) and densities lower than 0.915 g.cm−3 (JP 2002256006).
On the other hand, the use of ligands containing Group V and/or VI ligating atoms such as P, N, O or S with a suitable transition metal is not well known. WO 01/10876 A1 (BP Chemicals Ltd) discloses a process for the polymerisation and copolymerisation of olefins in the presence of a polymerisation catalyst or system comprising a source of a Group VIII transition metal such as nickel, and a bidentate phosphine ligand, the reactions being carried out at room temperature or 50° C. US 2003/0149198 A1 (Chevron Phillips Chemical Co) discloses the use of tridentate ligands of formula A with a transition metal to produce oligomers and/or polymers:
with Q1, Q2 and Q3 being O, S, N or P.
WO 02/04119 (BP Chemicals Ltd) discloses a process for the trimerisation of olefins in the presence of a catalyst comprising a source of a Group III to X transition metal, and a ligand containing at least one P, As or Sb atom bound to at least one hydrocarbyl or heterohydrocarbyl group having a polar substituent, but excluding the case where all such polar substituents are phosphane, arsane or stilbane. No polymerisation of olefins was obtained.
WO 2004/056479 A1 and WO 2004/056477 A1 were published after the priority date of the present application. These applications disclose an olefin tetramerisation process and an olefin trimerisation process respectively. In both cases a catalyst system substantially the same as the catalyst system used in the present invention was used. However, it has now been established that by using different reaction conditions (notably the reaction temperature) from those disclosed in the above applications, polymerization of olefinic compounds can be obtained in the presence of such catalyst systems.
It is accordingly an object of the present invention to provide a process for the polymerisation of olefinic compounds.